In some printers, gray output is produced by application of a mixture of colored inks, such as a mixture of cyan, magenta and yellow (CMY) inks. Where the application is successful, the output will appear neutral, i.e. the human eye will not perceive color. Unfortunately, “metamerism” is a phenomenon wherein the perceived hue of a given color changes with the type of illumination. This effect is particularly noticeable in the case of gray or near gray colors since the human threshold of perception of color difference is lower for gray or near gray colors than for more chromatic colors.
Some printers, such as “proofers” used in the commercial printing industry, may create output associated with a given lighting. Unfortunately, when the print output is viewed under different lighting conditions, metamerism operates to cause grays to appear to contain elements of color (i.e. a “color cast”). Accordingly, the output may vary from that which was intended, due to lighting conditions.